The printing industry is continually increasing the speed at which printed copy can be generated. Printing, forming, folding, and cutting operations are often performed by a continuous operation machine, feeding in a web of blank paper from a roll and ending with a printed, cut, and folded finished product, referred to as a signature.
One step in the process of producing the printed product may, for example, involve feeding multiple ribbons, layered one on top of the other, over a former board and into nip rolls below the former board as shows in FIG. 1. The former board 30, as is known in the art, provides, for example, for folding the ribbons in half longitudinally. The folded ribbons typically pass from the former board 30 into a nip roller 37 located below the former board 30. The ribbons are initially traveling in a first plane coincident with the former board 30. When the ribbons fold in half longitudinally, they fold into a plane perpendicular to the plane of the former board. After being folded over the former board 30, the ribbons may, for example, be cut into individual signatures by a cutting cylinder 34, followed by a decelerating and shingling procedure. For example, the cutting cylinder may deposit the signatures into a tape drive system 21 that directs the signatures into a fan wheels 40, 41 which decelerate the signatures and places them onto conveyor belts 55, 56 in shingled formation.
The ribbons may be fed to the former board 30 as shown in FIG. 2, as in known in the art. Several ribbons 2, 3, 4 are, for example, driven by nip rolls 5, 6, 7, respectively. The ribbons 2, 3, 4 are gathered at a gathering roll 8 and then traverse to the roll at the top of the former (the "RTF roll") 10 before traversing the former board 30.
A problem may arise with such a configuration because, due to the layering of ribbons on the gathering roll 8 and RTF roll 10, the outermost ribbons traverse a larger radius than the inner ribbons. For example, successive ribbons 2 and 3 traverse a radius at least one ribbon thickness greater than the ribbon upon which it rests. As a result, each ribbon 2, 3, 4 has a different local velocity as it traverses the RTF roll 10, the local velocity of successive ribbons increasing as the radius increases. Therefore, each ribbon experiences a tension and strain different from the tension and strain in the other ribbons. The uneven tensions and strains between the ribbons may result in lateral weaving, web shifting, wrinkling, fold variation, and print-to-cut errors.
Several attempts at eliminating the problem of unequal tension in the ribbons have been attempted. For example, making the outermost ribbon on the gathering roll 8 be the innermost ribbon on the RTF roll 10 attempts to compensate for the tension imbalance. Any imbalance which occurs due to experiencing an unequal radius on the gathering roll 8 is intended to be counterbalanced by making each ribbon experience a proportionally counteracting radius on the RTF roll 10. However, this solution fails to adequately address the problem because, for example, the spans 11, 12, 13 of the ribbons 2, 3, 4 preceding the gathering roll 8 is typically different from the span 14 after the RTF roll 10. Thus, proper counterbalancing of tension does not occur. Additionally, the amount of slippage in the nips and the flow of nip roll material at the gathering roll 8 and at the RTF roll 10 are usually different. Therefore, the tension in the ribbons is not counterbalanced properly.
It is an object of the present invention to provide a device to alleviate problems associated with feeding multiple web ribbons to a roll of the former section of a printing press.